1. Field of the Invention
The present invention generally relates to motion sensing and, more particularly, is concerned with an apparatus for sensing and accurately measuring translational and rotational motion of an object, such as a gun barrel during a firing event.
2. Description of the Prior Art
There are three distinct successive phases spanning from initial firing to final impact of a projectile which contribute to any observed dispersion or error in the accuracy of the projectile reaching the desired impact point. They are acceleration, transition and ballistic phases. The acceleration phase spans the initial period when the projectile is traveling down the gun barrel and the ballistic phase spans the period from when the projectile achieves free flight until it reaches impact. The transition phase spans the period from when the projectile leaves the barrel until it reaches free flight.
The measurement of factors contributing to error in projectile accuracy during the ballistic phase is well known and described in the prior art. However, in the prior art, measurements of contributing factors are lacking with respect to the acceleration and transition phases. One strategy for reducing the number of unknowns is to gain a better understanding of the acceleration phase so that the effects of the acceleration and ballistic phases can then be subtracted from the observed dispersion to determine the effect of the transition phase which appears to be the most difficult phase to measure directly.
It is generally known that projectile accuracy is very dependent on the interaction of the projectile and the gun barrel in the acceleration phase, especially at ejection of the projectile from the barrel. A number of approaches have been devised in the prior art to measure this interaction, but each has its own drawbacks.
In one approach, accelerometers are mounted on the end of the gun barrel to measure lateral motion. However, such devices are plagued with noise due to cross-axis sensitivity and do not measure velocities or displacements very well due to the integration required. In another approach, noncontacting magnetic (proximity) sensors are used. However, they are cumbersome and almost impossible to employ at the muzzle exit if significant recoil is present since the sensors will then extend into the blast area. In still another approach, a laser and quadrant detector is used in combination with a mirror mounted at the muzzle end. While this approach gives the best accuracies, it cannot distinguish between lateral displacements and changes in the pointing angle of the gun barrel. There are additional drawbacks associated with each of these approaches; only the major ones have been mentioned.
Consequently, if the aforementioned strategy for gaining an understanding of what the contribution of the transition phase is to projectile dispersion, a need exists for a technique to measure gun barrel motion, especially at ejection of the projectile, during the acceleration phase.